Aerojet Rocketdyne and its Rancho Cordova parent company this week fought back against suggestions that an engine it refurbished was the cause of a spectacular explosion of an unmanned rocket last October.

An executive with Orbital ATK Inc., speaking Tuesday at a space conference in Colorado, said the company believes excessive wear in the bearings of the engine was the cause of the Oct. 28 explosion that destroyed an Orbital Antares rocket a few seconds after liftoff from a NASA site in Virginia. The rocket was carrying cargo for the International Space Station. The comments were made by Ronald Grabe, Orbital’s executive vice president, at the annual Space Symposium in Colorado Springs.

Aerojet spokesman Glenn Mahone said the company’s own investigation, while still in progress, shows the engine bearings probably wore out because of “foreign object debris” in the engine. He said the debris appears to have come from the rocket’s propellant tanks or the propellant feeder system.

The engines propelling the Antares rocket were manufactured by the Soviet Union in the 1960s and modified by Aerojet.

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Mahone told The Sacramento Bee that Orbital’s claims were “incomplete and potentially misleading.” He said Aerojet was surprised that Orbital was commenting on possible causes while the various investigations are still underway.

A week after the explosion, Virginia-based Orbital said it would probably stop using the Aerojet-refurbished engines.

Shares of Aerojet’s parent, GenCorp Inc., closed Wednesday at $20.88, down 51 cents, on the New York Stock Exchange.